Nowadays, an office machine such as a multifunction peripheral and a scanner becomes an essential electronic device in the office. For continuously feeding a stack of documents to increase the scanning speed, automatic document feeders equipped with multifunction peripherals or scanners are introduced into the market. Generally, an automatic document feeder utilizes a sheet pick-up arm for successively feeding a stack of to-be-processed paper sheets into the inner portion of the main body of the office machine, so that the paper sheets can be further processed. Before the paper sheet is fed into a sheet-feeding channel of the automatic document feeder, a sheet stopping structure is disposed at an inlet of the automatic document feeder for stopping the paper sheet from entering the sheet-feeding channel. Due to the sheet stopping structure, the possibility of simultaneously feeding two or more paper sheets into the sheet-feeding channel by the sheet pick-up arm will be minimized. Moreover, for avoiding overlap or interference between successive paper sheets during the process of feeding the paper sheets, every two consecutive paper sheets fed into the automatic document feeder should be spaced from each other by a certain spacing interval. That is, after a previous paper sheet is fed into the sheet-feeding channel, a next paper sheet is stopped at the inlet by the sheet stopping structure. After the previous paper sheet is advanced for a constant distance, the next paper sheet is allowed to be introduced into the sheet-feeding channel.
FIG. 1 is a schematic perspective view illustrating a sheet stopping structure according to the prior art. The sheet stopping structure is disclosed in Taiwanese Patent No. 1290098. As shown in FIG. 1, the sheet stopping structure 1 comprises a sheet pick-up arm 11, a rotating shaft 12 and a sheet stopper 13. The sheet pick-up arm 11 comprises a protruding block 111 and a stopping slice 112. The protruding block 111 and the stopping slice 112 are both disposed on a lateral surface of the sheet pick-up arm 11. During operations, the rotating shaft 12 may drive rotation of the sheet pick-up arm 11 to a standby position or a sheet pick-up position. As shown in FIG. 1, the sheet pick-up arm 11 is in the standby position. The sheet stopper 13 comprises a pivotal part 131, a loading part 132 and a sheet stopping part 133.
Hereinafter, a process of performing a sheet pick-up operation by the conventional sheet stopping structure will be illustrated with reference to FIGS. 2A-2F.
First of all of, as shown in FIG. 2A, the sheet pick-up operation is not performed, and the sheet pick-up arm 11 is in the standby position. Meanwhile, since the sheet stopping part 133 is engaged with the protruding block 111, the sheet stopper 13 is maintained upright and fails to be pushed forward by the paper sheet S. Under this circumstance, the paper sheet S on the sheet-feeding channel is stopped by the sheet stopper 13.
Next, as shown in FIG. 2B, the sheet pick-up operation is ready, and the sheet pick-up arm 11 is rotated to the sheet pick-up position. Meanwhile, since the protruding block 111 of the sheet pick-up arm 11 is no longer engaged with the sheet stopping part 133, the sheet stopping part 133 is not hindered by the protruding block 111 but can be freely swung. Under this circumstance, the sheet stopping part 133 is stopped by the stopping slice 112 of the sheet pick-up arm 11, so that the sheet stopping part 133 fails to be swung toward the paper sheet S on the sheet-feeding channel. Consequently, the paper sheet S is not damaged by the sheet stopping part 133.
Then, please refer to FIGS. 2C and 2D. For performing the sheet pick-up operation, the paper sheet S is driven by the sheet pick-up arm 11 to be moved toward the internal portion of the automatic document feeder. As the paper sheet S is moved forwardly, the sheet stopping part 133 is pushed by the paper sheet S and then sunken under the sheet-feeding channel. Under this circumstance, the paper sheet S can be smoothly transported into the sheet-feeding channel without being stopped by the sheet stopping part 133.
Finally, please refer to FIGS. 2E and 2F. After the paper sheet S is completely transported across the sheet stopping part 133, the torque applied on the loading part 132 of the sheet stopper 13 will allow the sheet stopper 13 to be rotated about the pivotal part 131, so that the sheet stopping part 133 will be returned to the upright status. After the sheet pick-up operation is finished, the sheet pick-up arm 11 is lifted to the standby position, and the sheet stopping part 133 is engaged with the protruding block 111 again. Under this circumstance, the sheet stopping part 133 fails to be freely swung, so that other paper sheets S on the sheet-feeding channel will be continuously stopped by the sheet stopping part 133.
From the above discussions, the sheet stopping structure 1 is capable of stopping the paper sheets from entering the sheet-feeding channel by utilizing the sheet stopper 13 which can be engaged with the sheet pick-up arm 11.
The conventional sheet stopping structure 1, however, still has some drawbacks. For example, as previously described, the sheet stopping function is achieved only when the sheet stopping part 133 of the sheet stopper 13 is engaged with the protruding block 111 of the sheet pick-up arm 11. If the sheet stopping structure 1 is used for a long time period, the sheet stopper 13 is possibly suffered from deformation. Due to the deformation of the sheet stopper 13, the sheet stopping part 133 fails to be engaged with the protruding block 111 of the sheet pick-up arm 11, and thus the sheet stopping function of the sheet stopper 13 is lost. Under this circumstance, the use of the sheet stopping structure 1 may result in a multi-feeding problem of simultaneously feeding two or more paper sheets. For solving the multi-feeding problem, the sheet stopper 13 should be replaced with a new one. In other words, the conventional sheet stopping structure 1 is not user-friendly.
Therefore, there is a need of providing an improved sheet stopping structure so as to obviate the drawbacks encountered from the prior art.